1. Field of the Invention
This invention relates generally to electrical connectors. More particularly, the invention relates to an electrical connector which utilizes the mating of a tapered contact element with the conductive rim of a hole for providing an electrical connector function. The invention further relates to electrically connecting a first board, cable, wire, or other current carrying means which is coupled to the contact element, to a second board, cable, wire or other current carrying means on which the conductive rim of the hole is located. The invention further relates to the electrical connection of integrated circuit packages to circuit boards. More particularly, the invention relates to the packaging of integrated circuits for the removable mounting of the integrated circuits to host boards. The invention has application to all types of integrated circuits.
2. Prior Art
The electrical connector arts are crowded arts with many categories and subcategories of connectors. One such category are connectors which are used to connect two printed circuit boards (PCB). Within that category is a subcategory of connectors where the first PCB is a mother board, and the second PCB is a daughter board at right angles to the mother board, and the connection is a pluggable connection such that replacement of cards and/or expansion of the system is easily accomplished. The standard connectors for permitting such a non-permanent right angle interface require placing a first piece of hardware (e.g. in thee case of conventional inverted DIN type connectors, the pin or male part) on the mother board, and a second piece of hardware the mating female receptacle of a right angle connector) on the daughter board. While such connectors are typically successful for their purpose, as these connectors grow in size with high pin counts, bowing may occur in the connector during mating due to the high insertion force required resulting in difficult mating between the male and female connector shells. Further, these standard connectors are costly as they essentially require the use of two connector parts (a mating pair) for accomplishing a single connection. In fact, systems are often sold with the mother board portion of numerous connectors already attached to the mother board where daughter cards are only to be optionally provided in the event the system is expanded. Thus, where daughter cards are not ultimately used, unnecessary cost is suffered. In any event, it is desirable to provide an arrangement where connectors fixed to a daughter card could make electrical contact with the mother board directly without the added cost of a mating pair.
One solution to such a mother board/daughter board connection is proposed in U.S. Pat. No. 4,533,203 to Feldman et al., where a single connector having pins which are bent through a ninety degree turn and a two piece dielectric housing for housing the same are utilized in conjunction with contact pads on the mother board to establish contact. First ends of the pins are fixed to the daughter card while second ends are disposed at an oblique angle relative to the mother board to provide "wipe" action on the mating surface. Contact with the mother board is made between the angled second ends and contact pads on the mother board and aligning means are provided for aligning the angled pins and the pads. When contact is made, the bent portion of the pins deflects away from the mother board surface, and is permitted to do so by the housing which is enlarged around the area of deflection. With the provided arrangement, the two connector arrangement is obviated.
While the Feldman et al. patent does overcome some of the problems in the art, it does not address several matters of importance. First, the patent does not provide an adequate manner of maintaining the contact between the connector and the mother board, particularly where contact density is high. While a "keying block" is provided to establish alignment and to permit keying, there is no indication that the keying block also provides a means for establishing and maintaining contact. Second, because of the geometric nature of the angled pins and the contact pads, it is very possible that good contact at a sufficient contact force ("normal force") is not established between the pins and the circuit board. Third, where contact density is high, the size of the "engagement" or "hold-in" force (also called "mating" or "insertion" force) necessary for holding down the daughter board so that it may be locked relative to the mother board may very well be prohibitive. This is so, because the Feldman et al. configuration transmits the spring force directly to the contact pad on the mother card without any mechanical advantage. Thus, the "hold-in force" which is equal to the spring force, is also equal to the normal force. Fourth, because of the geometry and nature of the keying block, precise geometries are required, and if not met, may result in malfunctioning of the connector.
Many of the problems of the art are overcome by parent U.S. Pat. No. 4,966,556 which teaches a pluggable electrical connector having contact elements with first ends soldered to a daughter board, mid-sections which are bent through ninety degrees, and second ends which have a converging portion and which terminate in preferably compliant conical contact portions which make contact with the rims of contact-quality plated through holes of a mother board. By causing contact between the rim and the cone surface, normal forces greater than the mating force are generated. The connector housing preferably includes self-centering funnel openings adjacent the mother board for centering the converging portions of the contact elements therein in a nominal position and for acting as a preloading stop. The housing also preferably includes side-wall locking tabs which hold adjacent rows of contacts at identical fixing points relative to the ninety-degree bend to ensure identical spring parameters for all contact elements. By arranging the housing properly, the contact elements can be manufactured into preloaded spring contacts during assembly by bending and locking the first ends of the contacts past the side-wall locking tabs. Cams or retracting bars can be used with rows or individual contacts to create a ZIF connector and/or a selectively engaged pin enabled connector. Magnets, spring-loaded jack screws, or the like are used in conjunction with the connector to establish and maintain force during mating.
Parent Ser. No. 07/898,346 expands on parent U.S. Pat. No. 4,966,556 by providing additional board to board connectors with two contact portions, where both contact portions mate with holes in PCBs. Different embodiments of the springs as well as the contact portions of the the board to board connectors are provided. Additionally, embodiments are provided for tapered contact portion connectors which form a connection between a PCB and a ribbon cable, a flat cable, or a flex circuit. The provided embodiments teach the wide applicability of a connector where mating occurs between a tapered contact element and the rim of a circuit board.
Turning to the integrated circuit package (ICP) portion of the present invention, it is known the ICPs are substantially divided into two main categories: through-hole technology (THT); and surface mount technology (SMT). Examples of three common generic IC packages using the through-hole technology are seen in prior art FIGS. 1a-1c.
In FIG. 1a, a cross-section-through a plastic (N-type) dual-in-line package (DIP) is seen. The N type DIP consists of a circuit mounted on a lead frame having a desired number of leads, where the circuit is encapsulated within an electrically nonconductive plastic compound. The leads of the package of FIG. 1a are formed by stamping a flat sheet of lead material to form a lead frame, and bending the leads of the lead frame appropriately after the integrated circuit has been mounted on the lead frame and encapsulated, so that the leads may be inserted and soldered into mounting-hole rows of a circuit board.
A cross-section through a JD ceramic DIP is shown in FIG. 1b, The JD ceramic DIP has a hermetically sealed ceramic package with a metal cap and with side-brazed tin-plated leads. As with the N dual-in-line package, the leads of the JD ceramic DIP are intended for insertion and soldering into mounting-hole rows of a circuit board.
A partially cutaway top view of a GB pin-grid-array (PGA) ceramic package is seen in FIG. 1c. Like the JD ceramic dual-in-line package of FIG. 1b, the GB pin-grid-array ceramic package is also a ceramic package which is hermetically sealed with a metal cap. However, the "leads" of the GB pin-grid-array ceramic package are typically gold-plated pins which are arranged substantially in squares which surround the hermetically sealed ceramic package. The pins may be inserted and soldered into corresponding mounting holes of a circuit board, or as described in more detail hereinafter, and as is more commonly the case with GB pin-grid array ceramic packages, the package may be inserted into IC sockets which are inserted and soldered into the circuit board.
Examples of three common generic IC packages using the surface mount technology are seen in prior art FIGS. 2a-2c. In FIG. 2a, a perspective view of a D plastic small outline package is seen. The D plastic small outline package is manufactured in similar manner to, and corresponds closely to the N dual-in-line package, as it consists of a circuit mounted on a lead frame and encapsulated within a plastic compound. The only difference is that the free ends of the leads, instead of being straight for insertion into holes, are bent through approximately ninety degrees (i.e. "gull-wing" bent) for surface mounting.
A top view of an HQ quad flat package is seen in FIG. 2b. The HQ quad flat package is similar to the D plastic small outline package of FIG. 2a, except that the circuit is hermetically sealed, and the gull-wing bent leads are located on all four sides of the chip.
Turning to FIG. 2c, a partially sectioned side view of a FN plastic chip carrier package (PLCC package) is seen. As with the D plastic small outline package, the PLCC package consists of a circuit mounted on a lead frame and encapsulated within an electrically nonconductive compound. However, instead of two sets of parallel gull-wing bent leads, the leads are "J" leads which extend around the package in a square configuration. The J leads of the PCC package are surface mount soldered to solder lands.
Common to both the through hole packages and the surface mount packages is that in their basic forms, some kind of soldering process is used to fasten the ICPs to the host board for establishing electrical connection between the IC and the board. From a practical point of view, the soldering is a permanent process.
Although most, if not all, of the surface mount and through hole packages are intended to be soldered into contact with a circuit board, some subsets of the two main categories have been provided with IC sockets. The IC sockets effectively act as an interface or an interlocutor between the ICP and the circuit board. Typically, the IC sockets have contacts having first portions for individually contacting the leads of the ICP, and second portions, which are typically pins, for insertion into and contact with the circuit board. The IC sockets serve various functions, including avoiding the SMT process on a THT board by putting the SMT package in a socket which is soldered into through holes, and providing the ability to replace the IC with a different IC, which is particularly important in updating ROMs.
While IC sockets serve important functions, they have several drawbacks. First, because of their function, the IC sockets introduce an additional physical connection into each circuit. Instead of a single connection where the pins or leads of the ICP contact the circuit board directly, two connections are required; a first connection between the pins or leads and the IC socket, and a second connection between the pins or leads of the socket and the circuit board. This is a drawback, as every additional connection is a potential failure point, and thus system reliability is decreased. Second, the IC sockets are relatively costly. Third, special tools are often required to extract the ICPs from the IC sockets, and the ICPs can be damaged during extraction. A fourth drawback is that the IC sockets cause the ICPs to be lifted relative to the circuit board, thereby limiting the proximity in which two boards or the board and an additional object may be located.
Parent U.S. Pat. No. 5,160,270 overcomes many of the problems of the art by teaching an integrated circuit package with a plurality of contact element leads, each lead having a first portion for making electrical connection with the integrated circuit and a second tapered contact portion for mating with a conductive rim of the hole of a circuit board. In conjunction with the integrated circuit package, a fastener is provided for holding the tapered contact elements in mating relationship with the conductive rims. The tapered contact portion of the lead of the integrated circuit package may take any of various forms, as long as the lead is tapered and resilient so that proper mating with a conductive rim can be accomplished. Likewise, the fastener which holds the tapered contact elements in mating relationship with the conductive rims may take any of numerous forms. All that is required is that the fastener couple to both the circuit board and the integrated circuit package, and that the integrated circuit package be removable from the fastener.
It will be appreciated that the tapered contact elements of the parent U.S. Pat. Nos. 4,966,556 and 5,160,270 resiliently compress as they are pushed into the hole of a printed circuit board. While compressing, the surface of the contact element moves along the rim of the hole as it makes contact providing desired "wipe" and enhanced contact. While the contact forces and wipe provided by the tapered contact elements of the parent applications are suitable for most purposes, it will be appreciated that it is desirable to control many of the parameters which are considered of import in the connector arts. For example, the wipe at the connection, the axial spring rate of the connector, and the inductance of the connector are all considered important parameters, the control of which is desirable.